Aluminum alloys



Patented Oct. 31, 1933 UNITED STATES PATENT OFFICE ALUMINUM ALLOYS NoDrawing. Application September 21, 1932 Serial No. 634,151

2 Claims. (Cl. 75-1) The invention relates to aluminum base alloyscontaining magnesium and silicon and to alloys of this type which havesuperior resistance to corrosive agents.

5 The alloys to which this invention has reference are of the generaltype which contain about 0.4 to 2.0 per cent by weight of magnesium,about 0.6 to 2.5 per cent by weight of silicon. The alloys contain. atleast about 93 per cent by weight of aluminum and may, in addition,contain other alloying elements which may be added to the alloys togenerally harden them or to produce therein other specific Notable amongsuch alloying elements are nickel,

l5 manganese, etc. In the preferred form, these alloys are free fromcopper except as it may occur therein as an impurity, and it is to suchalloys that this invention relates. Such alloys are of the type known tothe aluminum arts as strong alloys, i. e., their particular usefulnessresides in their high strength and ductility, but these alloys have thefurther property of being comparatively resistant to corrosion,particularly in the heat-treated but unaged condition.

In normal condition and in the heat-treated and aged condition, thesealloys are somewhat deficient in resistance to corrosion when comparedwith other aluminum alloys of lesser strengths. The alloys to which thisinvention has reference are susceptible to thermal treatment, the mostcommon of which is a heat-treatment at temperatures of above about 500centigrade but below the temperature at which incipient fusion of thealloy takes place. This heat-treatment may be followed by a rapidcooling and then by artificial aging which comprises heating the alloyto temperatures of about 100 to 200 centigrade to further develop thealloys tensile properties.

With alloys of the above type I have experimented with the end inview ofincreasing their resistance to corrosion without materially de--tracting from the mechanical and other properties for which they arenoted. I have finally determined that small amounts of the metalzirconium, when added to these alloys, directly benefits theirresistance to corrosive agents without materially affecting theirmechanical properties or their workability. Nor does the addition ofthese small amounts of zirconium so disturb the equilibria existingbetween'the solid phases of the alloy as to decrease the known abilityof the alloys to respond to commercial heat-treating methods. The amountof zirconium which achieves these results when added properties.

to alloys of the type above described ranges from about 0.1 to about 1.0per cent by weight of the total alloy. Zirconium is a metal which meltsat relatively high temperatures and, therefore, I prefer to restrict theamount added when-. ever it is consistent with good results. About 0.2-to 0.3 per cent by weight of the total alloy is the preferred zirconiumcontent.

Before explaining the beneficial effects produced in the above-mentionedalloys by the addition thereto of small amounts of zirconium, it will benecessary to briefly explain the nature of the corrosion which takesplace in aluminum base alloys. All aluminum base alloys corrode to someextent when in contact with corrosive agents. This attack takes, interalia. two general forms. It is usually either of the intergranular'variety so named because the attack infiltrates into the alloy structurealong grain boundaries, or it is of the-pitting variety which does notproceed in any regular fashion and usually attacks only the metalsurface. In aluminum base alloys of the type above described bothvarieties of attack occur in varying proportions and intensity dependingupon the working and heat-treating history of the alloy. Theintergranular type of corrosion is the most serious in that it tends toundermine the structure and, therefore, the strength and ductility ofthe alloy. 35

The addition of zirconium in the amounts above named to the alloys abovedescribed results in a general beneficial change incorrosion-resistance, but it also has the further and most beneficialeffect of tending to reduce the amount of or the tendency tointergranular corrosion. This latter property of the zirconium isextremely beneficial and leads to measurable results. v

For example, the following test results maybe compared. In the table areshown the approximate compositions of four alloys.- All alloys were inthe form of rolled sheet when tested. Those alloys marked A had beenheat-treated for about about 5.3 per cent by weight of sodium chlorideand 0.3 per cent by weight of hydrogen peroxide. In the table oppositethe composition of each alloy is shown the tensile strength andelongation of the alloy before and after corrosion and the percentagechange in these properties caused by the corrosion.

1. A metallic alloy consisting of about 0.4 to 2.0 per centby weight ofmagnesium, about 0.6 to 2.5 per cent by weight of silicon, and about 0.1to 1.0 per cent by weight of zirconium, the balance being substantiallyaluminum and the said alloy being free from'copper except as animpurity.

Composition TePsfle g ggi fig per Elongationpercent in 2 inches Per entP r nt Percent Ba] 08 Before After cor- Percent Before After cor-Percent Mg Si Zr an corrosion lOSlOll change corrosion rosion change 0.6 1 A1 36, 290 36, 535 7 28. 5 24. 0 l5. 8 0. 6 l A] 46, 400 44. 795 3.5 l4. 3 5. 50 -61. 5 0. 6 1 0. 2 Al 35, 060 35, 015 -0 1 26. 3 26. 3 00. 6 l 0. 2 Al 45, 185 44, 180 -2 2 l5. 5 l4. 5 6 5 A study of theproperties shown in the table will demonstrate the efiect of thepresence of a small amount of zirconium. Those alloys containing nozirconium have deteriorated appreciably under the severe action of thecorrosion test while those containing zirconium have deteriorated littleif at all.

Having thus described my invention, I claim 2. A metallic alloyconsisting of about 0.4 to 2.0 per cent by weight of magnesium, about0.6 to 2.5 per cent by weight of silicon, and about 0.2 to 0.3 per centby weight of zirconium, the balance being substantially aluminum and thesaid alloy being free from copper except as an impurity.

LUDWIG J. WEBER.

